Google, Facebook, and Microsoft have publicly acknowledged the dangers of global warming, but last week they all sponsored a conference that promoted climate change denial to young libertarians.

All three tech companies were sponsors of LibertyCon, the annual convention of the libertarian group Students for Liberty, which took place in Washington, DC. Google was a platinum sponsor, ponying up $25,000, and Facebook and Microsoft each contributed $10,000 as gold sponsors. The donations put the tech companies in the top tier of the event’s backers. But the donations also put the firms in company with some of the event’s other sponsors, which included three groups known for their work attacking climate change science and trying to undermine efforts to reduce carbon emissions.